Department of Physics, University of Massachusetts at Amherst, Amherst, Massachusetts 01003, USA.
Langmuir. 2010 Feb 16;26(4):2317-24. doi: 10.1021/la9027404.
This paper explores the particle-level dynamics involved in the capture of gently flowing microparticles on adhesive planar surfaces, governed by electrostatic interactions. The work focuses on conditions which produce sustained microparticle rolling, useful for the development of microfluidic devices which steer analyte particles and cells for manipulation and separation. In the regime where particle-surface interactions dominate particle-particle interactions, capture of individual negative silica microspheres, for thousands of microspheres, is studied on three model surfaces: negative silica, a flat polycation layer adsorbed on silica producing a strong positive charge, and an electrostatically patchy surface containing 6% areal coverage of flat 10 nm polycation coils. The patchy surface possesses a net negative charge close to that of bare silica. On the patchy surface, sustained rolling is observed for a substantial population of 1 microm silica particles, the ones which happened to diffuse close to the surface. Here, the velocity is near 2 microm/s (for a wall shear of 22 s(-1).) Run lengths for particle rolling exceed several hundred micrometers (usually exceeding the length of the microscopic field of view), with more particles escaping diffusively from the interface than permanently arresting. By contrast, firm particle arrest, with very few instances of rolling and a short run length when rolling did occur, was observed on the fully cationic surface. On the bare silica surface, a small rolling population was observed; however, the average run length was shorter than on the patchy surface. This study demonstrated how a patchy surface that produces adhesion through localized attractions can facilitate rolling in a shear field. The physicochemical heterogeneity acts like a surface roughness or a rapidly binding ligand-receptor pair, transferring stress and imparting torque across the interface.
本文探讨了在静电相互作用控制下，轻柔流动的微粒在粘性平面表面上捕获的颗粒级动力学。这项工作侧重于产生持续微粒滚动的条件，这对于开发用于操纵和分离分析物颗粒和细胞的微流控设备非常有用。在颗粒-表面相互作用主导颗粒-颗粒相互作用的区域，在三种模型表面上研究了数千个负硅微球的单个负硅微球的捕获：负硅、吸附在硅上的带正电荷的平面聚阳离子层以及静电斑块表面含有 6%的平面 10nm 聚阳离子线圈的面积覆盖率。斑块表面具有接近裸露硅的净负电荷。在斑块表面上，观察到大量 1 微米硅颗粒的持续滚动，这些颗粒恰好扩散到靠近表面的位置。在这里，速度接近 2 微米/秒（壁剪切速率为 22 s(-1)）。颗粒滚动的运行长度超过几百微米（通常超过微观视野的长度），从界面扩散出的颗粒比永久捕获的颗粒多。相比之下，在完全阳离子表面上观察到牢固的颗粒捕获，滚动的情况很少，滚动发生时的运行长度很短。本研究表明，通过局部吸引力产生粘附的斑块表面如何在剪切场中促进滚动。物理化学异质性的作用类似于表面粗糙度或快速结合的配体-受体对，在界面上传递应力并传递扭矩。
